Question

Difficulty: HardDecimal Operations

Evaluate the following mathematical expressions involving decimals. What is the correct sequence of these expressions when ordered from least to greatest value?

  1. 10.15×40−14.4÷1.20.15 \times 40 - 14.4 \div 1.2
  2. 210.5−3.2×2.510.5 - 3.2 \times 2.5
  3. 3(4.2−1.8)÷0.6+0.5(4.2 - 1.8) \div 0.6 + 0.5
  4. 42.4×0.5+1.8÷0.32.4 \times 0.5 + 1.8 \div 0.3

Answer

The correct order from least to greatest is: 0.15×40−14.4÷1.20.15 \times 40 - 14.4 \div 1.2, followed by 10.5−3.2×2.510.5 - 3.2 \times 2.5, then (4.2−1.8)÷0.6+0.5(4.2 - 1.8) \div 0.6 + 0.5, and finally 2.4×0.5+1.8÷0.32.4 \times 0.5 + 1.8 \div 0.3.
Evaluating each expression using the correct order of operations yields final decimal values of 7.27.2, 2.52.5, −6.0-6.0, and 4.54.5. Arranging these values numerically from least to greatest provides the correct structural sequence.

Step-by-Step Solution

1
Evaluate the first expression: 2.4×0.5+1.8÷0.32.4 \times 0.5 + 1.8 \div 0.3.
1.2+6=7.21.2 + 6 = 7.2
According to the order of operations, multiplication and division are performed left-to-right before addition.
2
Evaluate the second expression: 10.5−3.2×2.510.5 - 3.2 \times 2.5.
10.5−8.0=2.510.5 - 8.0 = 2.5
Multiplication must be performed before subtraction.
3
Evaluate the third expression: 0.15×40−14.4÷1.20.15 \times 40 - 14.4 \div 1.2.
6.0−12=−6.06.0 - 12 = -6.0
Perform multiplication and division first. Then subtract the larger value from the smaller value, resulting in a negative number.
4
Evaluate the fourth expression: (4.2−1.8)÷0.6+0.5(4.2 - 1.8) \div 0.6 + 0.5.
2.4÷0.6+0.5=4+0.5=4.52.4 \div 0.6 + 0.5 = 4 + 0.5 = 4.5
Operations inside parentheses take highest priority, followed by division, and finally addition.
5
Order the evaluated results from least to greatest.
−6.0<2.5<4.5<7.2-6.0 < 2.5 < 4.5 < 7.2
Arranging the numerical values based on their algebraic magnitude provides the final sequence.

Key Concept

Order of Operations with Decimals

Alternative Method

Convert all terminating decimals to fractions (e.g., 0.5=120.5 = \frac{1}{2}, 0.3=3100.3 = \frac{3}{10}) before performing the operations to avoid decimal placement and alignment errors.
Estimated Time:1m 30s
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